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Fair Value Measurements - Summary of Fair Value Measurements of Company's Financial Assets and Liabilities (Details) - Fair Value, Recurring [Member] - USD ($)
$ in Thousands
Sep. 30, 2020
Dec. 31, 2019
Assets:    
Assets at fair value $ 183,998 $ 244,388
Liabilities:    
Derivative liability 1,259 969
Level 1 [Member]    
Assets:    
Assets at fair value 93,348 147,208
Level 2 [Member]    
Assets:    
Assets at fair value 90,650 97,180
Level 3 [Member]    
Liabilities:    
Derivative liability 1,259 969
Derivative Liability Exit Fee [Member]    
Liabilities:    
Derivative liability 1,259 969
Derivative Liability Exit Fee [Member] | Level 3 [Member]    
Liabilities:    
Derivative liability 1,259 969
Money Market Funds [Member]    
Assets:    
Assets at fair value 83,011 147,208
Money Market Funds [Member] | Level 1 [Member]    
Assets:    
Assets at fair value 83,011 147,208
Commercial Paper [Member]    
Assets:    
Assets at fair value 48,153 56,041
Commercial Paper [Member] | Level 2 [Member]    
Assets:    
Assets at fair value 48,153 56,041
Corporate Bonds [Member]    
Assets:    
Assets at fair value 39,274 33,134
Corporate Bonds [Member] | Level 2 [Member]    
Assets:    
Assets at fair value 39,274 33,134
U.S. Government-Sponsored Agency Bonds [Member]    
Assets:    
Assets at fair value 9,337  
U.S. Government-Sponsored Agency Bonds [Member] | Level 1 [Member]    
Assets:    
Assets at fair value 9,337  
Asset-Backed Securities [Member]    
Assets:    
Assets at fair value 3,223 8,005
Asset-Backed Securities [Member] | Level 2 [Member]    
Assets:    
Assets at fair value 3,223 $ 8,005
U.S. Treasury Notes [Member]    
Assets:    
Assets at fair value 1,000  
U.S. Treasury Notes [Member] | Level 1 [Member]    
Assets:    
Assets at fair value $ 1,000